This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The identification of the sub-population of cancer stem cells (CSC), responsible for cancer progression and metastasis (cellular target) and the discovery of proteins or pathways relevant to the malignant phenotype (molecular target), are very important to tailor appropriate systemic therapies. Prominin-1 (CD133), a cell-surface glycoprotein, named for its prominent location on the protrusion of cell membranes, has the potential to identify the cellular target and to constitute a molecular target for some types of cancer. CD133 has now been recognized as the most important CSC-associated marker identified so far, with increased expression in the CSC fraction of a large variety of human malignancies. The physiological function(s) of CD133 are unknown, except in the eye, where it is involved in photoreceptor disk morphogenesis. We have previously found that CD133 knockdown slowed cell growth, decreased cell motility, and reduced the capacity of human melanoma cells to metastasize. These data, together with the recent report of in vivo antitumor efficacy of an anti-CD133-drug conjugate in hepatocellular and gastric cancers11, strongly suggest that (i) CD133 is an important potential target per se, and (ii) targeting CD133 has potential clinical utility against CD133-expressing tumors. We are currently pursuing the following aims in our laboratory: A. Discovery of CD133 protein interactors by the yeast "two-hybrid" system. B. Discovery of additional (non-physical) interactions of CD133 with cellular genes and signaling pathways. C. To investigate the potential of anti-CD133 immunotoxins and of newly discovered CD133-interacting proteins or CD133-associated signaling pathways as targets for cancer therapeutic intervention.